Glycerokinase activity in human adipose tissue as related to obesity

The activity of the enzyme glycerokinase is low in mammalian adipose tissue, but high in certain forms of genetic obesity in rats and mice. This study was undertaken to determine if obese human subjects had higher glycerokinase activity than normal-weight subjects. Seventy-three randomly selected patients undergoing abdominal surgery were studied. Subcutaneous and omental adipose tissue was removed during surgery and the activity of the enzyme glycerokinase was measured in vitro under optimal conditions. The following observations were made: (1) the mean activity, when expressed per microgram DNA, was significantly (P less than 0.05) higher in obese subjects at both sites, yet no direct correlation to the degree of obesity was found; (2) the individual activity in morbidly obese patients undergoing gastroplasty correlated inversely with the rate of postoperative weight loss (r = -0.58, P less than 0.05); (3) glycerokinase activity was directly related (r = 0.59, P less than 0.01) to the rate of spontaneous glycerol release, and inversely related (r = -0.51, P less than .025) to the stimulation in glycerol release by norepinephrine; (4) the ratio glycerokinase/lipoprotein lipase in omental adipose tissue correlated with the degree of obesity (r = 0.43, P less than 0.05); (5) in nondiabetic male obese adults, the glycerokinase activity in subcutaneous adipose tissue inversely correlated with age (P = 0.05) and (6) the glycerokinase activity had two apparent Km values in three obese patients, in which it was studied kinetically. It is concluded that a small subsection of the obese population have a high potential for glycerol phosphorylation. In these individuals, weight loss is more difficult since they tend to reutilize the glycerol formed by lipolysis and net glycerokinase activity in their adipose tissue may reflect variations in lipid turnover.